Glycoproteins derived from the major histocompatibility complex (MHC) class Ib gene, HLA-G, were first described in human placentas, where they were located in cytotrophoblast (CTB) cells within and adjacent to the maternal decidua. Despite nearly two decades of intensive research, the role(s) of the products of this novel gene remain unclear, although most studies point to a role for HLA-G in regulating immune aspects of semiallogeneic pregnancy. The HLA-G gene has many novel features: the gene contains few polymorphisms in the coding region but multiple polymorphisms in the regulatory regions; at least 7 isoforms are generated by alternative splicing of mRNA derived from a single gene; HLAG has limited tissue distribution that includes high expression in placentas and also demonstrates differential isoform expression in CTB cell subpopulations. In this program application, three investigators from two institutions propose to study the role of placental HLA-G in pregnancy. All three, Dr. Joan Hunt (University of Kansas Medical Center, Kansas City, KS), Dr. Margaret Petroff from the same institution, and Dr. Carole Ober (University of Chicago, Chicago, IL) have extensive experience in reproductive immunology and have focused much of their research on MHC antigens in pregnancy. In Project I, Hunt will investigate mechanisms underlying isoform-specific expression and isoform-specific functions of HLA-G using newly generated recombinant soluble HLA-G glycoproteins and monoclonal antibodies to these proteins. In Project II, Petroff will examine co-expression of HLA-G isoforms and members of the B7 family, and will investigate implications for regulation of immune cell function using stably transfected cells expressing various combinations of HLA-G/B7 proteins. In Project HI, Ober will pursue functional aspects of HLA-G genotypes using newly developed allele-specific probes, and will explore relationships to diminished fertility. The program is supported by two Cores. Core A. Administration, directed by Hunt, will be responsible for assuring integration and publication of the outcomes of the experiments. Core B Tissue Collection and Genotyping, directed by Ober, will collect and supply all investigators with early gestation tissues and tissues from problem pregnancies. This core will also identify polymorphisms in genes relevant to each project. The investigators in this program fully expect that their close and systematic collaboration will comprise a powerful approach to elucidating critical aspects of HLA-G expression, regulation and function, and will ultimately lead to new and improved therapies for impaired fertility.